Epic: Support targeting iOS and Android with the .NET SDK

[dsplaisted]

This epic tracks the work to support targeting iOS and Android in the .NET SDK.

This includes work in the .NET SDK, MSBuild, and NuGet to support new TargetFrameworks, or other related work. It does not cover what will be delivered in the the iOS and Android workloads, nor the workload system itself (which is covered in #11164).

• NuGet - Support parsing operating system information from TargetFramework
• MSBuild - Add intrinsic functions to parse TargetFramework components (implemented by calling NuGet APIs)
• Parse TargetFramework into component properties in TargetFrameworkInference.targets (via new MSBuild intrinsic functions): Update Microsoft.NET.Sdk TargetFramework parsing to understand OS name and versions #11231
• Normalize TargetPlatformIdentifier casing
  • Windows
  • Android (.NET 6)
  • iOS and other Apple platforms (macOS, tvOS, watchOS) (.NET 6)
• Fail build if an unsupported or unknown operating system is specified in TargetFramework: Fail build if an unsupported or unknown operating system is specified in TargetFramework #11232
• Set default TargetPlatformVersion based on TFI, TFV, and TPI
  • For Windows: Set default TargetPlatformVersion for Windows #11233
  • For iOS and Android (in the corresponding workloads) .NET 6
• Support providing OS APIs from targeted platform: Support providing OS APIs from targeted platform #11234
• Add preprocessor symbols for OS: Automatically define preprocessor symbols for target platforms #11236
  • This also covers accumulating preprocessor symbols so that newer versions also include versioned symbols for the past
• Generate target platform assembly attributes: Generate target platform assembly attributes #11239
• Default OSMinimumVersion to TargetPlatformVersion, and error if it is higher than TargetPlatformVersion
• Support platform-specific OS minimum version attributes, translating them to OSMinimumVersion if current target matches
  • WindowsMinimumVersion -- .NET 6
  • IOSMinimumVersion -- .NET 6
  • AndroidMinimumVersion -- .NET 6
• Don't include OS info in runtimeconfig tfm: Don't include operating system info from TargetFramework in runtimeconfig.json tfm #11010
• Multitargeting support for WindowsDesktop
  • Support targeting WPF and WindowsForms using Microsoft.NET.Sdk (instead of Microsoft.NET.Sdk.WindowsDesktop): Shuffle property location wpf#3111
  • Import Windows desktop target when property is set #12106
  • Add warnings for WindowsDesktop targeting: Add warnings for WindowsDesktop targeting #11241
• Infer WinExe output type as appropriate Infer WinExe output type as appropriate #11398

.NET 6

Open design issues: #11275

• iOS / Android workloads: Support sdk-style projects for iOS / Android
  • Default item globs
  • Other defaults, and integration into Microsoft.NET.Sdk
• dotnet tools X net5.0 dotnet tools targeting Windows APIs #12055